Safety system for a liquid fuel tank

ABSTRACT

The invention relates to a plastic fuel safety system comprising (i) a liquid fuel tank which is fitted with a filler pipe that is equipped with a guide for a supply gun comprising a sealing device, (ii) a float valve, which is normally open, for the degassing and venting of the tank and (iii) a pipe for channelling the vapours and for fixing the maximum level of the liquid in the tank, said pipe connecting the upper part of the tank with an area located downstream of the sealing device. The invention also relates to a tank for a vehicle which is fitted with one such safety system and to an end plug for the filler pipe which, when in closed position, isolates the tank degassing and venting circuits.

[0001] The present invention relates to a safety system for a liquidfuel tank.

[0002] Many safety systems relating to fuel tanks have been describedand pertain in general to solving the problems associated with degassingof the tank, while it is being filled, and venting it during normalperiods when the engine is at rest and when it is in operation andconsuming this fuel. Added to these problems is the increasingly urgentneed, as regards protecting the environment, to recover the vapoursreleased during the abovementioned operations, by as far as possiblepreventing any leakage into the atmosphere.

[0003] U.S. Pat. No. 5,183,087 teaches how to degas a fuel tank providedwith a fill tube, with a degassing and venting valve connected to acanister and with a small-diameter pipe connecting the upper part of thetank to a guide located at the inlet of the fill tube, the function ofwhich is to initiate the closure of the fuel supply via the nozzle. Thisguide is provided with a sealing device and the pipe terminatesdownstream of the sealing device. In this system, degassing takes placeexclusively via the valve connected to the canister. This valve isnormally closed in the rest position and opens only under the effect ofa certain pressure in the tank.

[0004] However, the known systems have a number of drawbacks:

[0005] difficult control of the overpressure in the tank bringing aboutinopportune spillages and splashing when filling;

[0006] system ill-suited to recovering the vapours via the nozzle;

[0007] impossibility of closing off the fuel supply via the nozzle foran overfilling of less than 0.2 l.

[0008] The object of the invention is to remedy the drawbacks of theknown systems and to provide a system that allows:

[0009] filling without pressure in the tank;

[0010] elimination of fuel spillages and splashing;

[0011] standardization in the height of the fill tube for the variousfuels and methods of recovering the vapours;

[0012] the reduction in size of the system;

[0013] elimination of the anti-backflow and overfilling preventionvalves;

[0014] suppression of the vapour blast generated when venting, byelimination of the dense ball valve systems; and

[0015] a low cost to be maintained, of the order of magnitude or lessthan that of the conventional systems existing at the present time.

[0016] For this purpose, the invention relates to a safety system for aliquid fuel tank, comprising:

[0017] a) a fill tube mounted on this tank and provided, at its inletorifice, with a nozzle guide provided with a device for sealing withrespect to the external environment;

[0018] b) a float valve, mounted on the tank, capable of ensuringdegassing during an operation of filling this tank with-fuel, andlikewise venting it during periods of normal use of the tank;

[0019] c) a breather pipe for the vapours and for fixing the maximumlevel of liquid in the tank during filling, which pipe is immersed inthe top part of the tank, connecting this top part to the upper part ofthe fill tube, downstream of the sealing device, on the tank side;

[0020] in which the valve is normally open while the tank is beingfilled and also during periods of normal use of the tank and in whichthe “waterline” of the float is adjusted so that the valve is closedonly under two circumstances, namely when the tank is inclined beyond apredetermined limit, or even completely upside down, and during atransient movement of the fuel, the magnitude of which exceeds apredetermined value.

[0021] The invention relates to a safety system for a fuel tank, i.e. asystem that allows the fuel to be stored and handled in a manner that issafe both for the user and for the environment. Such a system protectsthe user from any-hazardous situation, in particular any risk ofexplosion, implosion, combustion or pollution, while not exposing theexternal environment to any leakage of liquid or emanation ofundesirable gases.

[0022] The tank to which the system according to the invention relatesconsists of a closed vessel, of various shapes, generally sealed withrespect to the outside and may be equipped with various internalaccessories or accessories that pass through the wall of the vessel. Thetank may contain any type of liquid fuel. In particular, it may containfuel for supplying motor-vehicle internal combustion engines,particularly petrol and diesel. By extension, it may also contain anyorganic liquid that would be used as fuel and/or oxidizer for the supplyof a fuel cell intended to generate an electric current for the purposeof supplying one or more engines consuming this type of energy.

[0023] The system according to the invention may be made of any suitablematerial used for producing a liquid fuel system. Examples of thesematerials are the various metals and plastics. A system according to theinvention may also comprise more than one particular material.

[0024] Preferably, the safety system according to the invention is madeof plastic. The term “plastic” is understood to mean any materialcomprising at least one synthetic resin polymer.

[0025] All types of plastic may be suitable. Particularly suitableplastics belong to the category of thermoplastics.

[0026] The term “thermoplastic” denotes any thermoplastic polymer,including thermoplastic elastomers, and also blends thereof The term“polymer” is understood to mean both homopolymers and copolymers(especially binary or ternary copolymers). Non-limiting examples of suchcopolymers are: random copolymers, linear block copolymers, other blockcopolymers and graft copolymers.

[0027] Any type of thermoplastic polymer or copolymer whose meltingpoint is below the decomposition temperature is suitable. Syntheticthermoplastics having a melting range spread over at least 10 degreesCelsius are particularly suitable. Examples of such materials are thoseexhibiting polydispersity of their molecular mass.

[0028] In particular, polyolefins, polyvinyl halides, thermoplasticpolyesters, polyketones, polyamides and copolymers thereof may be used.A polymer or copolymer blend may also be used, as may a blend ofpolymeric materials with inorganic, organic and/or natural fillers suchas, for example but not restrictively: carbon, salts and other inorganicderivatives, and natural or polymeric fibres. It is also possible to usemultilayer structures formed from stacked layers bonded together thatcomprise at least one of the abovementioned polymers or copolymers.

[0029] Polyvinyl halides and polyolefins are generally preferred.

[0030] One polymer often employed is polyethylene. Excellent resultshave been obtained with high-density polyethylene (HDPE).

[0031] The fill tube of the system according to the invention has thefunction of allowing the tank to be filled, without liquid leakage, froma point that is not in the immediate proximity of the tank. For example,it is common, in the case of private motor vehicles, for the fuel tankto be located at a somewhat inaccessible point and connected via a filltube to an orifice that can be closed off by a cap located at a pointeasily accessible from the vehicle's body.

[0032] According to the invention, the fill tube is provided, at itsinlet orifice, with a nozzle guide provided with a device for sealingwith respect to the external environment.

[0033] The nozzle is that fitted to the pumps of service stationsintended for supplying fuel, especially to motor vehicles.

[0034] According to the invention, the guide is provided with a devicefor sealing with respect to the external environment. This sealingdevice is capable of isolating the internal atmosphere of the tank andthat of the fill tube from the ambient atmosphere, even when the nozzleis inserted into the tube and passes along the said guide. The term“isolate” is understood here to denote acceptance of a slight leak ofaround 12 l/hour at an overpressure of 40 mbar with respect toatmospheric pressure when the nozzle is inserted into the guide and, inany case, less than 20 l/hour under the same pressure.

[0035] The operation of filling a tank with a liquid fuel is necessarilyaccompanied by an increase in the internal pressure in the tank. Whenthe latter includes a degassing circuit, the slight overpressure causedby the liquid newly introduced into the tank tends to be cancelled outthanks to a similar volume of gas that occupied the tank escapingtherefrom. In the case of volatile liquids, the gas that escapes will bea more or less homogeneous mixture of the gas present in the tank beforefilling and vapours coming from the partial vaporization of the liquidintroduced.

[0036] Moreover, during normal use of the tank, the volume of liquidfuel decreases as fuel is more or less regularly and/or continuouslyremoved. It is therefore necessary to provide and equip tanks withdevices allowing air to enter so as to compensate for the loss of liquidduring operation and thus prevent depressurization of the tank and thedangers inherent in this situation.

[0037] To obviate such risks, the role of the safety valve mounted on atank is to ensure that the tank is vented, in other words to allow it tobe opened in a programmed manner so as to carry out the two separatefunctions of degassing, when the tank is being filled, and ofventilation of the latter during normal use during which the fuel thatit contains is being consumed, or left in the tank for a certain storageperiod.

[0038] The safety system for a liquid fuel tank according to theinvention comprises a float valve, that is to say a device that can moveby sliding in a cylinder, which follows the level of fuel present in thetanks as soon as this level reaches the bottom rest position of thefloat in the cylinder. Such a valve is a device that, in collaborationwith the other elements of the safety system, contributes to keeping thetank on which it is mounted in a safe state for the user, that is to saya state in which the latter is protected from any hazardous situation,in particular any risk of explosion, implosion, combustion or pollution,while keeping the external environment protected from any leakage ofliquid or emanation of undesirable gases.

[0039] The system according to the invention also includes a breatherpipe for the vapours and for fixing the maximum level of liquid fuel inthe tank during filling. This pipe passes through the upper wall of thetank and is immersed inside the latter, in its top part, down to acertain level that corresponds to the maximum permitted upper level offuel in the full tank.

[0040] The breather pipe may pass through the upper wall of the tank atany point on the upper surface of the tank. In particular, it mayadvantageously pass through this wall at a point close or adjacent tothe valve.

[0041] The breather pipe connects the top part of the tank to the upperpart of the fill tube and is capable of removing most of the volume ofgases present in the tank, that is to say it has a diameter sufficientto allow the gases to escape without creating a substantial overpressureinside the tank.

[0042] This breather pipe terminates downstream of the sealing device ofthe nozzle guide present in the top of the fill tube. The term“downstream” should be understood here to mean that side of the sealingdevice located towards the tank.

[0043] According to the invention, the valve is open, in the normalsituation, during the operation of filling the tank, just like duringthe periods of normal use of the latter, when it is closed and the fuelis either being consumed or left in the tank for a certain storageperiod.

[0044] The “waterline” of the float of the valve is regulated so thatthe valve is closed only under two circumstances. The first of theseoccurs when the tank is inclined beyond a predetermined limit, or indeedis completely upside down. The second occurs during a transient movementof the fuel, the magnitude of which exceeds a certain predeterminedvalue.

[0045] An example of a float valve that is very suitable for the systemaccording to the invention is one that has two chambers, one including afloat and the other a volume acting as a container capable of trappingthe liquid fuel entrained by the vapours escaping from the valve. Such avalve is disclosed in French Patent Application No. 2000.09286.

[0046] The safety system described above is suitable for the varioustypes of geographical situation and the various types of nozzlesencountered in service stations that deliver fuel.

[0047] For example, it is well suited to the practice in North Americawhereby the fuel vapours are recovered in a large canister filled with amaterial that absorbs hydrocarbons.

[0048] It is also particularly well suited to the removal and recoveryof fuel vapours using what are called “active” nozzles, that is to saynozzles which themselves suck up the vapours, in order to store themand/or recover them from vehicles that have the safety system. Thesevehicles may be found mainly in Europe.

[0049] The sealing device conforming to the safety system according tothe invention may be made of any material capable of ensuring that thereis good sealing between the tank and the external atmosphere, includingwhen the spout of a fuel nozzle passes along it. The term “sealing” isunderstood here to mean accepting a slight leakage, of the same order ofmagnitude as that described above in the situation in which the nozzleis inserted into the guide.

[0050] One particular embodiment that has given good results is that inwhich this device is made of a flexible elastomer material having twoelements, the first, on the upstream side, consisting of severalcircular lips that bend back onto the outer surface of the pipe of thenozzle spout and the second, on the downstream side, consisting of anobturator that can open under the effect of the pressure when the end ofthe nozzle spout comes into contact with it. A device with two circularlips has given good results.

[0051] One possible embodiment of the obturator is a flat circular piecemade of elastomer material, slit in the manner of a star from its centreinto a certain number of radii that define lamellae of circular sectorshape that nevertheless seal against the gases when the said lamellaeare in the closed rest position, one against the other. An obturatorwith four lamellae in quarters has given excellent results. The term“sealing” here has the same meaning as previously.

[0052] When the tank is intended for storing fuels of high volatility, afirst variant of the system according to the invention, very suitablefor nozzles that are provided with fuel vapour suction devices, oneoutlet of the valve is connected, on the one hand, to a canister filledwith a material that absorbs the fuel vapours and a vapour degassingpipe connects, on the other hand, a second outlet of the valve to theupper part of the fill tube, upstream of the sealing device of the guideat a point close to the suction device of the nozzle. This degassingpipe is capable of removing most of the volume of gases that escape fromthe tank during an operation of filling the latter. Such a type ofvapour suction nozzle is also called an “active” nozzle. This system isparticularly advantageous when the active nozzle is of the type providedwith a suction device having a sleeve capable of surrounding the upperorifice of the tube via which the filling takes place. This type ofnozzle may be encountered more often in Europe than in North America.

[0053] The term “fuel of high volatility” is understood to mean lightfuels such as petrols of various grades, to the exclusion of heavieroils such as diesel or other fuel for diesel engines.

[0054] The outlets of the valve in question are, on the one hand, theoutlet for the gases of the venting circuit during periods of normaloperation and, on the other hand, the outlet for the gases of thedegassing circuit during filling. The latter outlet may, for example, belocated at the outlet for the gases of the container that traps theentrainments of liquid fuel when such a container is installed in thevalve used.

[0055] The expression “capable of removing most of the gases” has thesame meaning as explained above in the case of the breather pipe.

[0056] In the case of liquid fuels of high volatility and of nozzles notprovided with a fuel vapour suction system, a second variant of thesystem comprises a valve that is also connected to a canister filledwith a material that absorbs the fuel vapours. However, in thisparticular case, the volume of the canister, the size of the valve andthe diameter of the pipe connecting the valve to the canister aredimensioned so that the latter is capable of removing by itself most ofthe volume of gases that escape from the tank during the fillingoperation. In this case, in addition to absorbing the gases duringventing of the tank in normal use, the canister also absorbs the gasesleaving the tank during filling. This situation may be encounteredmainly in North America.

[0057] A third variant of the system according to the invention,suitable for fuels of low volatility, comprises a valve, the outlet ofwhich runs into a canister filled with a material that absorbs the fuelvapours. In this case, there is generally only a single outlet of thevalve. This system may be encountered both in Europe and in NorthAmerica.

[0058] In the case of fuels of low volatility, a fourth variant, analternative to the third variant, consists in the outlet of the valverunning into the atmosphere, without passing via a canister. Thisvariant is more particularly suitable for European systems. The outletinto the atmosphere may be direct, on the valve itself It may also takeplace via a device that prevents solid particles from being introducedinto the tank or by any other suitable device such as a pipe or anyremoval circuit.

[0059] According to a fifth variant of the system according to theinvention, in accordance with the third and fourth variants, a vapourdegassing pipe connects a second outlet of the valve to the upper partof the fill tube, upstream of the sealing device of the guide, at apoint close to a suction device of the nozzle, and is capable ofremoving most of the volume of gases that escape from the tank during anoperation of filling the latter.

[0060] The meanings of the terms “sealing” and “upstream” and of theexpression “capable of removing most of the volume of gases that escapefrom the tank” have here again the same meanings as those explainedabove.

[0061] An alternative system in accordance with each of the fivevariants explained above again consists in that the degassing pipe alsoserves for introducing fuel into the tank. In this situation, this pipeextends the fill tube. It may penetrate the tank at any point on itsupper surface. Preferably, it penetrates the tank via the same openingin the wall of the latter as a pump and/or gauge module.

[0062] The breather and/or degassing pipes generally have a shape thatintroduces a siphon between the tank and the top of the fill tube. As anoption, when the need for it arises, for example in the case of designswith little space, the system according to the invention may alsocomprise breather and/or degassing pipes that do not include a siphon.

[0063] The invention also relates to a liquid fuel tank for a vehicleequipped with a system according to any one of the embodiments detailedabove.

[0064] Finally, the invention also relates to a fill tube cap of asystem according to the variants that include a degassing pipe connectedto the upper part of the fill tube, upstream of the sealing device, thecharacteristic of which is to include, at its end inside the tube, acircular projection capable, when this cap is in the closed position, ofclosing off the lip of the flexible seal furthest upstream and ofisolating, in a sealed manner, the degassing pipe from the assemblyformed by the fill tube and the first vapour breather pipe. The sealinghere is understood to mean both against the vapours and against liquidfuel.

[0065] FIGS. 1 to 4 that follow have the purpose of illustrating theinvention, without in any way limiting its scope.

[0066]FIG. 1 illustrates schematically a safety system for a liquid fueltank in a version suitable for European countries.

[0067] In this figure, a high-density polyethylene tank (12) containingliquid fuel is provided with a fill tube (10), with a degassing andventing valve (6), that includes a liquid trapping container (18), saidvalve being connected via the pipe (7) to a canister (8) filled withactive carbon and via a degassing pipe (4) to the upper orifice (3) ofthe fill tube (10). A vapour breather pipe (19) connects the overhead ofthe tank (12) to a region (1) of the tube (10) located immediatelydownstream of the sealing device (2). This sealing device (2) comprisesa flexible seal. The breather pipe (19) penetrates the tank via the sameorifice as that made in the wall of the latter for the valve (6) and isimmersed in the overhead of the tank (12) down to a level (5) that fixesthe maximum permitted liquid fuel level in the tank. FIG. 1 also shows aservice station nozzle (14) that delivers fuel, engaged in the top ofthe tube (10) and passing through the sealing device (2) in such a waythat the end (17) of the delivery spout is located downstream of theseal (2).

[0068] The details of the operation of the system shown in FIG. 1 are asfollows. Starting from the initial situation in which the tank (12) isclosed off by a cap (not shown) for closing off the fill tube (10) andthe tank in the normal rest situation, with no fuel being removed, thecap closing off the inlet (3) of the fill tube (10) is opened so as tocarry out a refuelling operation.

[0069] The nozzle (14) is then inserted into the inlet (3) of the tube(10) and mechanically forced so as to penetrate the seals of the sealingdevice (2) and to open and pass through the obturator located in thedownstream part of this device. This nozzle (14) has, at the end of itsspout (17) inserted into the tube (10) downstream of the seal of thesealing device (2), an inlet orifice serving as fuel inflow cut-off tripsensor. Thanks to the seals of the sealing device (2), the ambient aircan no longer enter the orifice of the trip system of the nozzle (14).The obturator is opened by the spout (17) that forces open the wall cutinto the form of a cross, preventing filling when it is in the closedposition. This arrangement of the obturator makes it possible to forcethe nozzle (14) to assume a correct position-so as to deliver the fuelinto the tank (12) and to position the spout (17) of the nozzle (14)downstream of the sealing device (2).

[0070] Next, the user performs the operation of opening the nozzle (14)placed correctly in the tube (10) and petrol starts to be delivered intothe tank (12). In order for the nozzle (14) not to initiate and causethe inflow of petrol to stop, air and/or petrol vapours escape via thebreather pipe (19), the part pipe immersed in the tank down to the level(5), the gas pocket (16), the valve (6), the degassing pipe (4) and theatmosphere close to the inlet (3).

[0071] At the same time, the volume of petrol introduced via the tube(10) replaces the volume of gas present in the pocket (16) of the tank(12). This volume of gas escapes, as explained above, via the valve (6)and the degassing pipe (4).

[0072] At the start of the pipe (7) of the valve (6) there is a Venturidevice that introduces a certain head loss into the connection betweenthe valve (6) and the canister (8), so as to let through to the canisteronly a small amount of gas, substantially less than that flowing in thepipes (19) and (4). This arrangement prevents the active carbon thatfills the canister (8) from being unnecessarily saturated during thefilling operation.

[0073] During filling, the overpressure within the tank (12) relative toatmospheric pressure remains very low and determined only by the lowhead-loss characteristics of the open passages of the valve (6) and ofthe degassing pipe (4).

[0074] The gases escaping into the atmosphere at the inlet (3) of thenozzle are sucked up by means of an active system comprising a sleeve(not shown) surrounding the top of the nozzle (14) and the inlet (3) andconnected to a suction pump of the service station where the gases arecollected.

[0075] The petrol level (13) in the tank rises and ends up by beingflush with the orifice of the breather pipe (19), at the height of thelevel (5). At this moment, the nozzle (14) no longer receives air or gascoming from the pocket (16) and the inlet orifice of the spout (17) issubjected to a slight vacuum, which consequently activates the automaticvacuum-sensitive device on the nozzle (14) and cuts off the inflow ofpetrol.

[0076] Since the valve (6) remains open, the very slight overpressurepresent in the tank during filling is balanced with the atmosphericpressure via the degassing pipe (4) and the outlet (3). After the capfor closing off the orifice of the tube (10) has been closed, pressurebalancing in the tank is continued by means of the pipe (7) and thecanister (8).

[0077]FIG. 2 shows schematically a safety system for a liquid fuel tankin a version suitable for North America.

[0078] In this figure, a high-density polyethylene tank (12) containingliquid fuel is provided with a fill tube (10), with a degassing andventing valve (6), that includes a liquid trapping container (18), saidvalve being connected via the pipe (7) to a large canister (8) filledwith active carbon. A vapour breather pipe (19) connects the overhead ofthe tank (12) to a region (1) of the tube (10) located immediatelydownstream of the sealing device (2). This sealing device (2) comprisesa flexible seal. The breather pipe (19) penetrates the tank via the sameorifice as that made in the wall of the latter for the valve (6) and isimmersed in the overhead of the tank (12) down to a level (5) that fixesthe maximum permitted liquid fuel level in the tank. FIG. 2 also shows aservice station nozzle (14) that delivers fuel, engaged in the top ofthe tube (10) and passing through the sealing device (2) in such a waythat the end (17) of the delivery spout is located downstream of theseal (2). This spout (17) is pierced by openings (not shown) that areconnected to an external fuel vapour suction device.

[0079] The details of the operation of the safety system of FIG. 2 areas follows. Starting from the initial situation in which the tank (12)is closed off by a cap for closing off the fill tube (10) and the tankin the normal rest situation, with no fuel being removed, the capclosing off the inlet (3) of the fill tube (10) is opened so as to carryout a refuelling operation.

[0080] The nozzle (14) is then inserted into the inlet (3) of the tube(10) and mechanically forced so as to penetrate the seals of the sealingdevice (2) and to open and pass through the obturator located in thedownstream part of this device. This nozzle (14) has, at the end of itsspout (17) inserted into the tube (10) downstream of the seal of thesealing device (2), an inlet orifice serving as fuel inflow cut-off tripsensor. Thanks to the seals of the sealing device (2), the ambient aircan no longer enter the orifice of the trip system of the nozzle (14).The obturator is opened by the spout (17) that forces open the wall cutinto the form of a cross, preventing filling when it is in the closedposition. This arrangement of the obturator makes it possible to forcethe nozzle (14) to assume a correct position so as to deliver the fuelinto the tank (12) and to position the spout (17) of the nozzle (14)downstream of the sealing device (2).

[0081] Next, the user performs the operation of opening the nozzle (14)placed correctly in the tube (10) and petrol starts to be delivered intothe tank (12). In order for the nozzle (14) not to initiate and causethe inflow of petrol to stop, air and/or petrol vapours escape via thebreather pipe (19), the pipe part immersed in the tank down to the level(5), the gas pocket (16), the valve (6), the pipe (7), the canister (8)and the venting outlet (11).

[0082] At the same time, the volume of petrol introduced via the tube(10) replaces the volume of gas present in the pocket (16) of the tank(12). This volume of gas escapes, as explained above, via the valve (6)and the canister (8).

[0083] During filling, the overpressure within the tank (12) relative toatmospheric pressure remains very low and determined only by the lowhead-loss characteristics of the open passages of the valve (6), of thepipe (7) and of the canister (8).

[0084] The vapours coming from the pocket (16) are removed by thebreather pipe (19) from the orifice located at the level (5), the inletof the region (1) and the suction holes (not illustrated) of the spout(17) of the nozzle (14).

[0085] The petrol level (13) in the tank rises and ends up by beingflush with the orifice of the breather pipe (19), at the height of thelevel (5). At this moment, the nozzle (14) no longer receives air or gascoming from the pocket (16) and the inlet orifice of the spout (17) issubjected to a slight vacuum, which consequently activates the automaticvacuum-sensitive device on the nozzle (14) and cuts of the inflow ofpetrol.

[0086] Since the valve (6) remains open, the very slight overpressurepresent in the tank during filling is balanced with the atmosphericpressure via the pipe (7), the canister (8) and the outlet (11).

[0087]FIG. 3 illustrates the cross section of a nozzle (14) whose spout(17) has been correctly inserted into a sealing device (2) of a tube(10). This device is provided with two flexible seals (20) and (21) andwith a star-shaped obturator having four quarters (22). The figure alsoshows the inlet (1) of the breather pipe (19) and the orifice (3) of thedegassing pipe (4).

[0088]FIG. 4 shows a cross section in a tube/guide/cap assembly in theclosed position. It shows the projecting end (23) of the cap (24) thatcloses off the connection between the fill tube (10) and the degassingpipe (4).

1. Safety system for a liquid fuel tank, comprising: a) a fill tubemounted on this tank and provided, at its inlet orifice, with a nozzleguide provided with a device for sealing with respect to the externalenvironment; b) a float valve, mounted on the tank, capable of ensuringdegassing during an operation of filling this tank with fuel, andlikewise venting it during periods of normal use of the tank; c) abreather pipe for the vapours and for fixing the maximum level of liquidin the tank during filling, which pipe is immersed in the top part ofthe tank, connecting this top part to the upper part of the fill tube,downstream of the sealing device, on the tank side; characterized inthat the valve is normally open while the tank is being filled and alsoduring periods of normal use of the tank and in that the “waterline” ofthe float is adjusted so that the valve is closed only under twocircumstances, namely when the tank is inclined beyond a predeterminedlimit, or even completely upside down, and during a transient movementof the fuel, the magnitude of which exceeds a predetermined value. 2.System according to the preceding claim, characterized in that thesealing device is made of a flexible elastomer material having twoelements, the first, on the upstream side, consisting of circular lipsthat bend back onto the outer surface of the pipe of the nozzle spoutand the second, on the downstream side, consisting of an obturator thatcan open under the effect of the pressure when the end of the nozzlespout comes into contact with it.
 3. System according to either of thepreceding claims, suitable for liquid fuels of high volatility and fornozzles that are provided with fuel vapour suction devices,characterized in that one outlet of the valve is connected, on the onehand, to a canister filled with a material that absorbs the fuel vapoursand in that a vapour degassing pipe connects, on the other hand, asecond outlet of the valve to the upper part of the fill tube, upstreamof the sealing device of the guide at a point close to the suctiondevice of the nozzle, this degassing pipe being capable of removing mostof the volume of gases that escape from the tank during an operation offilling the latter.
 4. System according to either of claims 1 and 2,suitable for liquid fuels of high volatility and for nozzles that arenot provided with fuel vapour suction systems, characterized in that thevalve is connected to a canister filled with a material that absorbs thefuel vapours and in that the volume of the canister, the size of thevalve and the diameter of the pipe connecting the valve to the canisterare dimensioned in order to be able to remove most of the volume ofgases that escape from the tank during the filling operation.
 5. Systemaccording to either of claims 1 and 2, suitable for liquid fuels of lowvolatility, characterized in that the outlet of the valve runs into acanister filled with a material that absorbs the fuel vapours.
 6. Systemaccording to either of claims 1 and 2, suitable for liquid fuels of lowvolatility, characterized in that the outlet of the valve runs into theatmosphere, without passing via a canister.
 7. System according to claim5 or 6, characterized in that a vapour degassing pipe connects a secondoutlet of the valve to the upper part of the fill tube, upstream of thesealing device of the guide, at a point close to a suction device of thenozzle, and is capable of removing most of the volume of gases thatescape from the tank during an operation of filling the latter. 8.System according to any one of claims 3 to 7, characterized in that thedegassing pipe also serves for introducing fuel into the tank andpenetrates the tank via the same opening in the wall of the latter as apump and/or gauge module.
 9. Liquid fuel tank for a vehicle equippedwith a system according to any one of claims 1 to
 8. 10. Fill tube capfor a system according to any one of claims 3, 7 and 8, characterized inthat it includes, at its end inside the tube, a circular projectioncapable, when the cap is in the closed position, of closing off the lipof the flexible seal furthest upstream and of isolating, in a sealedmanner, the degassing pipe from the assembly formed by the fill tube andthe first vapour breather pipe.